How to bake normal map if the models intersect?
To bake from an object with is slightly outer of your lowpoly mesh, you need to increase the ray distance option in the bake panel:



Blender bake using a ray casting. If the ray distance is 0, the ray starts from the lowpoly surface. So, if this surface is inside the highpoly mesh, the ray meets nothing.

With a higher value for the ray distance the ray starts farther to the outside of the lowpoly so that it can hit the highpoly surface.

Practically speaking you may need to tune this value (not too high, not to low) so that the ray does not hit unwanted surfaces of the highpoly mesh.